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Oil-spill dispersants may have hurt Gulf food chain, study says

A boat motors July 31, 2010, through oil sheen from the Deepwater Horizon spill off East Grand Terre Island, where the Gulf of Mexico meets Barataria Bay.

AP/file

JANET McCONNAUGHEYThe Associated Press

Published: Tuesday, July 31, 2012 at 5:15 p.m.

Last Modified: Tuesday, July 31, 2012 at 5:15 p.m.

NEW ORLEANS — A study on possible effects of the 2010 BP oil spill indicates dispersants may have killed plankton — some of the ocean's tiniest plants and creatures — and disrupted the food chain in the Gulf of Mexico, one of the nation's richest seafood grounds.

Scientists who read the study said it points toward major future effects of the spill. One called its findings scary.

For the study, Alabama researchers pumped water from Mobile Bay into 53-gallon drums, then added oil, dispersant or both in proportions found during the oil spill to simulate the spill's effects on microscopic water-life in the bay.

Over more than 12 weeks in 2010, BP's well spewed nearly 200 million gallons of oil into the Gulf of Mexico. The company used more than 1.8 million gallons of dispersants — more than 770,000 gallons of it at the oil's source on the ocean floor — to break up the oil into tiny droplets. Earlier research hadn't found significant problems for the environment and marine life, but dispersants had never before been used a mile underwater or in such large amounts.

The researchers found that, within days, the numbers of plant-like phytoplankton and ciliates — plankton that use hairlike cilia to move — increased under an oil slick. But they dropped significantly in the drums with dispersant or dispersed oil, while the numbers of bacteria increased. The study was published today in PLoS ONE, one of the peer-reviewed journals in the online Public Library of Science.

"In those tanks, all of the energy seems to get trapped in the bacterial side. There were lots of bacteria left but no bigger things. It's like the middle part of the food web is taken away," said lead researcher Alice Ortmann of the University of South Alabama and Dauphin Island Sea Lab.

Microbes are too small for fish to eat. Ciliates, on the other hand, "graze" on microbes. Phytoplankton and cilates both get eaten by larger zooplankton, which are fodder for tiny crustaceans that, in turn, get eaten by small fish.

Brian Crother, a biology professor at Southeastern Louisiana University, called the findings scary, though limited because the experiments spanned only five days. "If these guys are on the money, they have pointed to something really disastrous happening in the Gulf," he said.

The study was extremely well done, said Michael Crosby, senior vice president for research at Mote Marine Laboratory in Sarasota, Fla. "You've got to look at the impact on the ecosystem as a whole, rather than individual species," he said.

It is also, he said, more evidence for what he has thought all along: that the Gulf of Mexico's food web is in danger. "If you go a couple steps beyond their findings, I think we're going to see these things happening and it's going to take years for them to be seen," he said.

Ortmann said she and her colleagues, including scientists at Auburn University, were surprised that dispersant alone had such a big effect on plankton.

Carbon is a basic part of most life on earth, and an earlier study at Dauphin Island Sea Lab found that plankton quickly gulped down oil from the spill.

Crother said the new study makes clear that the damage to plankton was from dispersant, not oil. "These guys have shown ... that the carbon available from that dispersant is not easily utilized for energy at the bottom of the food chain," he said.

Still, other research indicates that "fish did very well in 2010," Ortmann said. There's no indication that the food web was completely disrupted, but it might have been interrupted in certain areas, she said.

More research is being done to try to understand the spill's actual impact, she said.

Crosby noted that some environmental effects weren't seen for years after the tanker Exxon Valdez hit a reef and broke open off Alaska in 1989, causing what was then the nation's largest spill, 11 million gallons.

The late 1980s had been marked by record commercial harvests of herring, but by 1993, the number of spawning adults had dropped by three-quarters. Disease, ocean changes, contaminants, competition from other fish and increasing numbers of humpback whales are being studied as possible reasons that the species has never recovered.

"The herring population in Prince William Sound didn't collapse until four years after the Exxon Valdez," Crosby said. "It has never recovered. Never."

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